Hypokalemic periodic paralysis

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Hypokalemic periodic paralysis (hypoPP) is a disorder that causes occasional episodes of muscle weakness and sometimes a lower than normal level of potassium in the blood. The medical name for low potassium level is hypokalemia.

Causes

HypoPP is congenital. This means it is present at birth. In most cases, it is passed down through families (inherited) as an autosomal dominant disorder. In other words only one parent needs to pass the gene related to this condition on to their child in order for the child to be affected.

In some cases, the condition may be the result of a genetic problem that is not inherited.

Unlike other forms of periodic paralysis, people with hypoPP have normal thyroid function. But they have a very low blood level of potassium during episodes of weakness. This results from potassium moving from the blood into muscle cells in an abnormal way.

Risk factors include having other family members with periodic paralysis. The risk is slightly higher in Asian men who also have thyroid disorders.

Symptoms

Symptoms include attacks of muscle weakness or loss of muscle movement (paralysis) that come and go. There is normal muscle strength between attacks.

Attacks usually begin in the teen years, but they can occur before age 10. How often the attacks occur varies. Some people have attacks every day. Others have them once a year. During attacks the person remains alert.

The weakness or paralysis:

Most commonly occurs at the shoulders and hips

May also affect the arms, legs, muscles of the eyes, and muscles that help with breathing and swallowing

Occurs off and on

Most commonly occurs on awakening or after sleep or rest

Is rare during exercise, but may be triggered by resting after exercise

May be triggered by high-carbohydrate, high-salt meals or drinking alcohol

Usually lasts 3 to 24 hours

Other symptoms may include:

Eyelid myotonia (a condition in which after opening and closing the eyes, they cannot be opened for a short time)

Exams and Tests

The health care provider may suspect hypoPP based on a family history of the disorder. Other clues to the disorder are muscle weakness symptoms that come and go with normal or low results of a potassium test.

Between attacks, a physical examination shows nothing abnormal. Before an attack, there may be leg stiffness or heaviness in the legs.

During an attack of muscle weakness, blood potassium level is low. This confirms the diagnosis. There is no decrease in total body potassium. Blood potassium level is normal between attacks.

During an attack, muscle reflexes are decreased or absent. And muscles go limp rather than staying stiff. Muscle groups near the body, such as the shoulders and hips, are involved more often than the arms and legs.

Treatment

The goals of treatment are relief of symptoms and prevention of further attacks.

Muscle weakness that involves the breathing or swallowing muscles is an emergency situation. Dangerous irregular heartbeats (heart arrhythmias) may also occur during attacks. Any of these must be treated right away.

Potassium given during an attack may stop the attack. Potassium can be taken by mouth. But if weakness is severe, potassium may need to be given through a vein (IV).

Taking potassium supplements will not prevent attacks.

Avoiding alcohol and eating a low-carbohydrate diet may help.

A medicine called acetazolamide may be prescribed to prevent attacks. Your provider may tell you to also take potassium supplements because acetazolamide may cause your body to lose potassium.

If acetazolamide does not work for you, other medicines may be prescribed.

Outlook (Prognosis)

HypoPP responds well to treatment. Treatment may prevent, and even reverse, progressive muscle weakness. Although muscle strength starts out normal between attacks, repeated attacks may eventually cause worsening and permanent muscle weakness between attacks.

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